My old guild put out a list in January for the year. Snacks were 'assigned' to all members by month. Three members per month were responsible. i.e. Jan, Betty and Joan had January....Pam, Judy and Treva had February....and so on...take the number of members...divide by the number of months....and assign away. If you weren't going to be at guild on your assigned month, it was YOUR responsibility to trade-off with someone....